Regeneration of indigenous woody species under the canopies of tree plantations in Central Ethiopia

The hypothesis that tree plantations may foster the regeneration of native woody species, was tested through studies of understory floristic composition, height-class dis- tribution of naturally regenerated seedlings and saplings of indigenous woody species, and soil seed banks in the native and exotic tree plantations in Central Ethiopia. A total of 70 plots, having 10 x 10 m area each, were studied in six monoculture plantation stands of four exotic species, i.e. Cupressus lusitanica (2 stands of different age), Eucalyptus globulus, Pinus patula, P. radiata and Juniperus procera, an indigenous coniferous species. Ages of the plantations ranged between 14 and 42 years. Soil seed bank analysis was also undertaken from soil sam- ples collected in each of the 70 plots to examine the similarity between the soil seed flora and aboveground vegetation. Vegetation diversity was assessed through analyses of floristic compo- sition, species richness and abundance. A total of 37 naturally regenerated indigenous woody species were recorded beneath all plantation stands, with densities ranging between 1630 and 18270 individuals ha-1. There was considerable variation among plantation stands/species with respect to the density of naturally regenerated native woody species. Generally, seedling popu- lations were the most abundant components of the regeneration in most of the plantation stands, forming 85% of the total regeneration count. A total of 68 plant species represented by 53 herbs, eight woody species and seven grasses were recorded in the soil seed bank from all stands. Similarity between the soil seed banks and aboveground flora (both seedlings and lar- ger plants) was very low implying that the role of soil seed banks in the regeneration is low and dispersal of seeds from the adjacent natural forest plays an important role in the process. These results support the concept that forest plantations can foster the regeneration of native woody species and increase biodiversity in the plantation stands, if seed sources are available in the vicinity of the plantations. Resumen: Con el fin de probar la hipotesis de que las plantaciones de arboles pueden fo- mentar la regeneracion de especies lenosas nativas, se estudio la composicion floristica del so- tobosque, la distribucion de clases de altura de plantulas y juveniles resultantes de la regen- eracion natural de especies lenosas nativas, y los bancos de semillas en el suelo de plantaciones de arboles nativos y exoticos en el centro de Etiopia. En total se estudiaron 70 parcelas de 10 × 10 m en rodales de plantaciones monoespecificas de cuatro especies exoticas: Cupressus lusi- tanica (dos rodales de diferente edad), Eucalyptus globulus, Pinus patula, P. radiata, y de la conifera nativa Juniperus procera. Las edades de las plantaciones fluctuaron entre 14 y 42 anos. El banco de semillas en el suelo fue analizado con base en muestras tambien recolectadas en cada una de las 70 parcelas con el fin de examinar la similitud entre la flora del banco de semillas y la vegetacion establecida. La diversidad de la vegetacion fue evaluada por medio de analisis de la composicion floristica, la riqueza de especies y la abundancia. Se registraron en total 37 especies nativas lenosas naturalmente regeneradas bajo todos los rodales de las